1. Field of the Invention
Embodiments of the invention relate generally to the field of injection molding systems and to methods of using such systems. More particularly, an embodiment of the invention relates to a molding apparatus coupled to a characterization computer and to methods of characterizing a fluid within the mold space of a molding apparatus.
2. Discussion of the Related Art
Prior art molding or casting systems are known to those skilled in the art. For instance, a conventional injection molding system injects fluid into a mold space through several openings, thereby filling the mold space with the fluid, which solidifies to the shape of the mold space.
A problem with molding and casting is the time required to fill a mold space. To reduce the time necessary to fill a mold, the dynamic properties of fluids have been characterized and the results used to improve the processes of charging the molds, as well as the molds themselves. For instance, the interior surfaces of molds defining their corresponding mold spaces have been equipped with conductivity sensors. As the fluid fills the mold space, the conductivities measured by the sensors can be observed to drop in the case of materials having resistances less than the unfilled portion of the molds, thereby providing data on the behavior of the advancing molten front.
Meanwhile, composite materials are being utilized in an increasing number of articles of manufacture. A preform may be placed in a mold space prior to filling to generate a composite product. The use of carbon preforms is common in the production of composite parts through injection molding. One example of such a composite part is a pick up body bed for a vehicle. Such carbon preforms or mats provide the most weight saving in, for example, a car or airplane part, which in turn saves the most fuel. Carbon fiber composites save about 65% by weight over standard steel structural parts in a car. Glass fiber composites save about 35% over steel.
Molding with preforms presents a problem in that a preform in a mold space presents a physical barrier to the fluid charging the mold. This can increase the time required to fill a mold and/or result in defects such as voids in the finished product. To reduce the time necessary to fill a mold space that includes a preform, and to reduce the instance of defects, there is an ongoing need to characterize and optimize the dynamic properties of fluids in such preform containing molds. However, a serious problem with characterizing the dynamic properties of fluids in preform containing molds is that the previous approach of using conductivity sensors becomes inoperable in the case where the preform has a resistance less than the unfilled portion of the mold space. More specifically, in the manufacture of composite molded products, carbon or glass fiber preforms can be placed inside the mold space. Preforms made of carbon or glass fiber are conductive, thus rendering characterization techniques using conductivity sensors inoperative. Therefore, what is needed is an approach that solves the problem of how to characterize the dynamic front of fluid in the case of a mold space that contains a conductive preform.
An unsuccessful previous approach to solving this problem has been to recess the sensor(s) below the interior surface of the mold space. However, this approach causes wetting or surface tension problems which prevent the sensor from responding consistently. Furthermore, recessed conductive sensors require about four hours to test the filling of a mold space, and therefore they are not realistic for modeling industrial processes that need to be operated in a cost effective manner.
Heretofore, the requirements of characterizing the dynamic fluid front within a mold space containing a preform have not been fully met. What is needed is a solution that addresses this requirement.